Insert: Beyond our Solar

System

Deployment of the Hubble Space Telescope in Earth orbit, April 24, 1990

The 300-meter radio telescope at Arecibo, Puerto Rico

Hertzsprung-Russell diagram Shows the relation between stellar

• Brightness (absolute magnitude) and• Temperature

Diagram is made by plotting (graphing) each star's • Luminosity (brightness) and• Temperature

Hertzsprung-Russell diagram

Parts of an H-R diagram • Main-sequence stars

• 90% of all stars• Band through the center of the H-R diagram• Sun is in the main-sequence

• Giants (or red giants) • Very luminous• Large• Very large giants are called supergiants• Only a few percent of all stars

Hertzsprung-Russell diagram Parts of an H-R diagram

• White dwarfs• Fainter than main-sequence stars• Small (approximate the size of Earth)• Lower-central area on the H-R diagram• Not all are white in color• Perhaps 10% of all stars

Hertzsprung-Russell diagram

The Orion Nebula is a well-known emission nebula

A faint blue reflection nebula in the Pleiades star cluster

Stellar evolution Two opposing forces in a star are

Gravity – contractsThermal nuclear energy – expands

StagesBirthMain-sequence stage

• 90% of a star's life is in the main-sequenceRed giant stageBurnout and death

• white dwarf, neutron star, or a black hole

Evolutionary stages

Stellar evolution

Stellar remnants White dwarf

• Small and Dense• Spoonful weighs several tons

Neutron star • Gravitational force collapses atoms

• Electrons combine with protons to produce neutrons• Pea size sample weighs 100 million tons• First one discovered in early 1970s Crab nebula

(remnant of an A.D. 1054 supernova)

Crab Nebula in the constellation Taurus

Stellar remnants Black hole

• More dense than a neutron star• Intense surface gravity lets no light escape• As matter is pulled into it

• Becomes very hot• Emits x-rays

• Likely candidate is Cygnus X-1, a strong x-ray source

Binary Pair with a Red Giant and a Black Hole

Galaxies Other galaxies

• Existence was first proposed in mid-1700s by Immanuel Kant

• Four basic types of galaxies • Spiral galaxy

• Arms extending from nucleus• About 30% of all galaxies• e.g., Milky Way

Face-on view of the Milk Way Galaxy

Edge-on view of the Milk Way Galaxy

Great Galaxy, a spiral galaxy, in the constellation Andromeda

Galaxies Other galaxies

• Four basic types of galaxies • Barred spiral galaxy • Elliptical galaxy • Irregular galaxy

The study of light Doppler effect

The apparent change in wavelength of radiation caused by the relative motions of the source and observerUsed to determine

• Direction of motion• Increasing distance – wavelength is longer

("stretches")• Decreasing distance – makes wavelength shorter

("compresses")

The Doppler effect

Red shifts Doppler effect

• Change in the wavelength of light emitted by an object due to its motion

• Movement away stretches the wavelength • Light appears redder

• Movement toward “squeezes” the wavelength• Light shifted toward the blue

• Expanding universe • Most galaxies exhibit a red Doppler shift

Raisin bread analogy of an expanding universe

Big Bang theory

Accounts for galaxies moving away from us

Universe was once confined to a "ball" that was • Supermassive• Dense• Hot

Big Bang theory Big Bang marks the inception of the

universe • Occurred about 15 billion years ago• All matter and space was created

Matter is moving outward Fate of the universe

• Two possibilities • Universe will last forever• Outward expansion sill stop and gravitational;

contraction will follow

Big Bang theory Fate of the universe

• Final fate depends on the average density of the universe

• If the density is more than the critical density, then the universe would contract

• Current estimates point to less then the critical density and predict an ever-expanding, or open, universe

End of Chapter 16